In locations requiring all-night or all-day surveillance, such as the strong rooms of financial institutions or places used to store important confidential industrial information, or to give a more familiar example, ATMs (automated teller machines) installed in banks and various kinds of retail outlets including convenience stores, a surveillance camera, sound-collecting microphone, and so forth, are set up near whatever is being monitored, and multimedia data such as continuously captured video data and voice data can be checked ex post facto when necessary. With this kind of surveillance system, the above-described operation is implemented by storing captured video data, voice data, and the like, on a storage medium (recording medium) such as a hard disk at regular intervals, and reading that data when necessary.
Recently, due to the deteriorating public safety situation in Japan, a trend has appeared of increasing the locations monitored by surveillance systems, with surveillance cameras being installed in such places as railway stations, shopping malls, and unmanned warehouses with no inward or outward movement of goods. A common characteristic of these surveillance systems is that, since the objects monitored span a wide range, it has become necessary to install a plurality of surveillance cameras and so forth, and surveillance systems have become larger in scale. The need for higher precision of surveillance data has also increased, and improvements have generally come to be made in video data resolution and voice data quality. There has thus been a marked increase in the quantity of surveillance data recorded as compared with the situation heretofore.
However, as there are limits to the capacity of recording media, in order to perform fixed-period storage of video and other multimedia data, it is necessary for data recorded in the past to be erased after the elapse of a fixed period or when the vacant recording medium capacity becomes insufficient, and for new data to be recorded in that vacant space, or for surveillance data to continue to be stored endlessly (hereinafter referred to as “endless recording”) by sequentially overwriting old data with new data.
One conventional multimedia data recording apparatus is a video recording apparatus that makes it possible to maintain the quality of important video, and also to record video information for a long period on a medium of limited storage capacity, by storing video information whose quality the user wants to ensure in uncompressed form, and storing other video information in compressed form (see Patent Document 1, for example). This video recording apparatus records video information on a video recording medium, records the occurrence of a burglary, robbery, traffic accident, fire, or similar incident (hereinafter referred to generically as an “event”) on the video recording medium, and increases the available recording medium capacity by reading from the video recording medium, from among the video information recorded on the recording medium, video information unrelated to an event, and compressing and rerecording that read video information.
When an event occurs, both recorded data of the event (hereinafter referred to as “event data”), and also data immediately prior to the occurrence of the event (hereinafter referred to as “pre-event data”), are important as material for identifying the cause of the event. One multimedia data recording apparatus that performs recording of pre-event data (hereinafter referred to as “prerecording” or “pre-event recording”) is a surveillance image recording apparatus that saves pre-event data in an area separate from the normal recording area (see Patent Document 2, for example). By saving (copying) pre-event data, this apparatus prevents important surveillance data from being erased after the elapse of a fixed period.    Patent Document 1: Unexamined Japanese Patent Publication No. 2000-13745    Patent Document 2: Unexamined Japanese Patent Publication No. HEI 9-46636